Process for producing bisphenol a

ABSTRACT

There is provided a process for producing bisphenol A exhibiting a stable hue without undesired coloration even when treated at an elevated temperature. In the process for producing bisphenol A by reacting acetone with phenol in the presence of an acid-type ion exchange resin as a catalyst and then subjecting the reaction mixture to a reduced-pressure distillation to recover the bisphenol A from a fraction discharged from a bottom of distillation column, said process comprises: washing said acid-type ion exchange resin filled in a reactor with phenol before used in the reaction; and distilling a phenol solution obtained after the washing together with a fraction obtained from a top of the distillation column to recover phenol.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a process for producingbisphenol A exhibiting a stable hue. The thus produced bisphenol A isuseful as raw materials of polycarbonate resins, epoxy resins,polyarylate resins or the like.

[0003] 2. Background Arts

[0004] As well known in the arts, bisphenol A [2,2-bis(4-hydroxyphenyl)propane] is an important compound useful as raw material of engineeringplastics such as polycarbonate resins and polyarylate resins, or epoxyresins. Recently, the demand for the above compound tends to be more andmore increased. In particular, when used as raw material ofpolycarbonate resins, the bisphenol A has been required to exhibit astable hue without undesired coloration even when it is treated at anelevated temperature.

[0005] It is also known that the bisphenol A is produced by condensingphenol with acetone in the presence of an acid-type ion exchange resinas a catalyst. In this case, the acid-type ion exchange resin is usuallyswelled with water and packed in a reactor. After packing, the ionexchange resin is washed with water to remove acid substances therefrom,and then washed with phenol prior to its use in the reaction.Conventionally, the phenol used for the washing has been usually mixedwith a reaction mixture discharged from outlet of the reactor in orderto recover and purify the phenol. For this reason, the thus producedbisphenol A inevitably contains acid substances, resulting indeteriorated hue thereof.

DISCLOSURE OF THE INVENTION

[0006] The present invention has been made in view of the aboveproblems. An object of the present invention is to provide a process forproducing bisphenol A exhibiting a stable hue without undesiredcoloration even when treated at an elevated temperature.

[0007] As the result of extensive studies, the present inventors havefound that the above object is achieved by removing acid substances froma phenol solution obtained after washing the acid-type ion exchangeresin. The present invention has been accomplished based on thisfinding.

[0008] Thus, the present invention provides a process for producingbisphenol A by reacting acetone with phenol in the presence of anacid-type ion exchange resin as a catalyst and then subjecting thereaction mixture to a reduced-pressure distillation to recover thebisphenol A from a fraction discharged from a bottom of distillationcolumn, comprising:

[0009] washing said acid-type ion exchange resin filled in a reactorwith phenol before using the ion exchange resin in the reaction; and

[0010] distilling a phenol solution obtained after the washing togetherwith a fraction obtained from a top of the distillation column forrecovery of phenol.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in detail below.

[0012] First, the respective steps of the process for the production ofbisphenol A is described.

[0013] Step (1): Reaction Step

[0014] Bisphenol A is produced by reacting acetone with an excess amountof phenol in the presence of an acid-type ion exchange resin as catalystand, if required, alkylmercaptan as co-catalyst. As the suitableacid-type ion exchange resin as catalyst, there may be generally usedsulfonic acid-type cation exchange resins. Examples of such sulfonicacid-type cation exchange resins include sulfonated styrene divinylbenzene copolymers, sulfonated crosslinked styrene polymers, phenolformaldehyde-sulfonic acid resins, benzene formaldehyde-sulfonic acidresins or the like. These sulfonic acid-type cation exchange resins maybe used alone or in the form of a mixture of any two or more thereof.

[0015] The suitable alkylmercaptan used as co-catalyst are suchmercaptans having a C₁-C₁₀ alkyl group. Examples of the alkylmercaptansinclude methylmeicaptan, ethylmercaptan, propylmercaptan,octylmercaptan, cyclohexylmercaptan or the like. Among thesealkylmercaptans, ethylmercaptan is especially preferred. Meanwhile,these alkylmercaptans may be used alone or in the form of a mixture ofany two or more thereof.

[0016] The above reaction may be desirably conducted by a fixed-bedcontinuous or batch method, though not limited thereto. When thereaction is conducted by fixed-bed continuous method, the liquid hourlyspace velocity (LHSV) used therein is usually in the range of 0.2 to 30Hr⁻¹, preferably 0.5 to 6 Hr⁻¹.

[0017] As to the other reaction conditions, the reaction temperature is60 to 100° C.; the molar ratio of phenol to acetone is 6 to 13; and themolar ratio of acetone to mercaptan is 13 to 25.

[0018] The resultant reaction mixture contains, in addition to bisphenolA, unreacted phenol, unreacted acetone, catalysts, by-produced water,alkylmercaptan, and other by-products such as organic sulfur compoundsand colored substances.

[0019] Step (2): Recovery of By-Produced Water and Unreacted RawMaterials

[0020] Then, the reaction mixture obtained in the step (1) is distilledunder reduced pressure to remove unreacted acetone, by-produced water,alkylmercaptan, a part of unreacted phenol and the like from a top ofdistillation column and obtain a liquid mixture containing bisphenol A,phenol, etc., from the bottom thereof. The reduced-pressure distillationmay be conducted at a temperature of 70 to 180° C. under a pressure of6.7 to 80.0 kPa. Upon such a distillation, the unreacted phenol issubjected to azeotropy, and removed out of the reaction system from thetop of the distillation column.

[0021] Step (3): Concentration of Bisphenol A

[0022] The bottoms obtained by removing the above substances from thereaction mixture, is then distilled under reduced pressure to removeunreacted phenol therefrom and concentrate bisphenol A containedtherein. The thus obtained concentrated residual solution is used as araw material of the subsequent crystallization step. The concentrationconditions are not particularly restricted, but the concentrationprocess may be usually conducted at a temperature of 100 to 170° C.under a pressure of 5.3 to 66.7 kPa. When the temperature is less than100° C., it is necessary to keep the reaction system under high vacuumcondition. On the contrary, when the temperature is more than 170° C.,an additional heat-removal step is required upon conducting thesubsequent crystallization step. The concentration of bisphenol Acontained in the concentrated residual solution is in the range of 20 to50% by weight, preferably 20 to 40% by weight. When the concentration ofbisphenol A contained in the concentrated residual solution is less than20% by weight, the recovery percentage of bisphenol A becomes lowered.On the contrary, when the concentration of bisphenol A in the residualsolution is more than 50% by weight, it is difficult to transport aslurry obtained after the crystallization step.

[0023] Step (4): Crystallization

[0024] The concentrated residual solution obtained in the step (3) iscooled to a temperature of 40 to 70° C. to crystallize an adduct ofbisphenol A and phenol (hereinafter referred to merely as “phenoladduct”), thereby obtaining a slurry. The cooling is conducted due toheat removal caused by evaporating water added to external heatexchanger and crystallizer. Next, the slurry-like concentrated residualsolution is subjected to filtration, centrifugal separation, etc., andseparated into the phenol adduct and a crystallization mother liquorcontaining by-products. The thus obtained crystallization mother liquormay be directly or partially recycled to the reactor, or recovered inthe form of phenol and isopropenyl phenol by subjecting whole or partthereof to alkali decomposition. Alternatively, a part or whole of thecrystallization mother liquor may be isomerized and recycled as rawmaterial to the crystallization step (refer to Japanese Patent Laid-openNo. 6-321834).

[0025] Step (5): Heat-Melting of Phenol Adduct

[0026] The 1:1 adduct of bisphenol A and phenol obtained in the step (4)in the form of crystals, is heat-melted at a temperature of 100 to 160°C. to obtain a liquid mixture.

[0027] Step (6): Recovery of Bisphenol A

[0028] The liquid mixture obtained in the step (5) is distilled underreduced pressure to remove phenol and recover bisphenol A therefrom. Thereduced-pressure distillation is conducted at a temperature of 150 to190° C. under a pressure of 1.3 to 13.3 kPa. In addition, the removal ofresidual phenol may be conducted by known methods such assteam-stripping.

[0029] Step (7): Granulation of Bispherol A

[0030] The molten bisphenol A obtained in the step (6) is formed intodroplets using a granulating apparatus such as spray dryer, and cooledand solidified to obtain an aimed product. The droplets are produced byspraying, spreading or the like method, and cooled with nitrogen, air orthe like.

[0031] In the present invention, the acid-type ion exchange resin filledin the reactor is washed with phenol before used in the reaction, and aphenol solution obtained after the washing (hereinafter referred tomerely as a “washing phenol solution”) is distilled together with afraction (containing acetone, by-produced water, phenol andalkylmercaptan) obtained from a top of the reduced-pressure distillationcolumn used in the above step (2) to recover phenol therefrom andrecycle the recovered phenol. In the distillation, only one distillationcolumn may be used to separate the mixture into respective components byvarying the distillation conditions. Alternatively, several distillationcolumns may be used to separate the mixture into respective components.The washing phenol solution and the fraction obtained from the top ofthe above reduced-pressure distillation column may be continuously orintermittently mixed together. In any case of the continuous andintermittent mixing methods, the distillation may be conducted in such amanner that the ratio of phenol contained in the washing phenol solutionto that recovered from the fraction obtained from the top of thereduced-pressure distillation column is within the range of 1:0.01 to1:2.

[0032] The thus recovered phenol contains no acid substances and istherefore reusable as the raw material.

[0033] Meanwhile, the washing phenol solution may be temporarily storedbefore use.

[0034] Next, the process of the present invention will be described inmore detail below. However, these examples are only illustrative and notintended to limit the present invention thereto.

EXAMPLE 1

[0035] A packed bed-type reactor having an inner diameter of 13 mm and aheight of 560 mm was filled with 74 cc of a water-swelled sulfonicacid-type cation exchange resin (“DIAION-104H” available from MitsubishiChemical Corp.). While maintaining the reaction temperature at 60° C.,the sulfonic acid-type cation exchange resin filled in the reactor waswashed with 80 cc of water and then with 110 cc of phenol. The resultantsolution obtained after washing the ion exchange resin with phenol wasrecovered in a flask. It was confirmed that the recovered washing phenolsolution contained about 49% by weight of water and 3 weight ppm ofsulfonic acid (in terms of p-toluenesulfonic acid).

[0036] The washing phenol solution was heated under ordinary pressure toremove water therefrom, and then treated at 170° C. under reducedpressure to recover phenol therefrom and purify the recovered phenol. Asa result, it was confirmed that the thus purified phenol contained about1,000 weight ppm of water, but did not contain any sulfonic acid.

[0037] After completion of washing the above catalyst, phenol, acetoneand ethylmercaptan were fed from an inlet of the reactor and passedtherethrough at a liquid hourly space velocity (LHSV) of 1 Hr⁻¹ in suchamounts that the molar ratio of phenol to acetone was 10 and the molarratio of acetone to ethylmercaptan was 20, thereby conducting thereaction at 80° C. (acetone conversion rate: 75%).

[0038] The purification and hue of the reaction solution was evaluatedby the following method.

[0039] The reaction solution was distilled at 170° C. under reducedpressure to remove unreacted acetone, by-produced water, ethylmercaptanand a part of unreacted phenol therefrom. The remaining solution wasfurther distilled at 154° C. under reduced pressure to remove an excessamount of phenol therefrom and concentrate the bisphenol A containedtherein up to 40% by weight. The thus obtained concentrated solution wascooled to 43° C. to crystallize and precipitate an adduct of bisphenol Aand phenol, and then subjected to solid-liquid separation The obtainedadduct of bisphenol A and phenol in the form of crystals was treated at170° C. under a pressure of 4 kPa to remove phenol therefrom and obtainbisphenol A.

[0040] The obtained bisphenol A was heated at 175° C. in air for 30minutes and visually observed using an APHA standard solution toevaluate a hue thereof. As a result, it was confirmed that the hue ofthe obtained bisphenol A was as good as 10 APHA.

EXAMPLE 2

[0041] The same procedure as in EXAMPLE 1 was repeated except that asulfonic acid-type cation exchange resin (“K1221” available from Bayer AG.) was used. As a result, it was confirmed that the washing phenolsolution contained about 49% by weight of water and 7 weight ppm ofsulfonic acid (in terms of p-toluenesulfonic acid).

[0042] The washing phenol solution was heated under ordinary pressure toremove water therefrom, and then treated at 170° C. under reducedpressure to recover phenol therefrom and purify the recovered phenol. Asa result, it was confirmed that the thus purified phenol contained about950 weight ppm of water, but did not contain any sulfonic acid.

[0043] The thus produced bisphenol A exhibited a hue as good as 15 APHA.

COMPARATIVE EXAMPLE 1

[0044] The same procedure as in EXAMPLE 1 was repeated except that amixture of 200 cc of the reaction solution and 20 cc of the phenolsolution used for the washing in EXAMPLE 1 was treated to recover andpurify bisphenol A As a result, it was confirmed that the thus producedbisphenol A exhibited a hue of 25 APHA.

COMPARATIVE EXAMPLE 2

[0045] The same procedure as in EXAMPLE 1 was repeated except that amixture of 200 cc of the reaction solution and 10 cc of the phenolsolution used for the washing in EXAMPLE 2 was treated to recover andpurify bisphenol A As a result, it was confirmed that the thus producedbisphenol A exhibited a hue of 30 APHA.

INDUSTRIAL APPLICABILITY

[0046] In accordance with the present invention, in the process forproducing bisphenol A by reacting acetone with phenol in the presence ofan acid-type ion exchange resin as catalyst and then subjecting thereaction mixture to a reduced-pressure distillation to recover thebisphenol A from a fraction discharged from a bottom of distillationcolumn, it is possible to produce bisphenol A exhibiting a stable huewithout undesired coloration even when treated at an elevatedtemperature by washing said acid-type ion exchange resin filled in areactor with phenol before used in the reaction; and distilling a phenolsolution obtained after the washing together with a fraction obtainedfrom a top of the distillation column to recover phenol therefrom.

What is claimed is:
 1. A process for producing bisphenol A by reactingacetone with phenol in the presence of an acid-type ion exchange resinas a catalyst and then subjecting the reaction mixture to areduced-pressure distillation to recover the bisphenol A from a fractiondischarged from a bottom of distillation column, comprising: washingsaid acid-type ion exchange resin filled in a reactor with phenol beforeused in the reaction; and distilling a phenol solution obtained afterthe washing together with a fraction obtained from a top of thedistillation column to recover phenol.
 2. A process according to claim1, wherein said acid-type ion exchange resin is a sulfonic acid-typecation exchange resin.
 3. A process according to claim 1, whereinalkylmercaptan is used as a co-catalyst of said acid-type ion exchangeresin.
 4. A process according to claim 1, wherein the reaction betweenphenol and acetone is conducted by a fixed-bed continuous or batchmethod.